Existing asthma-related quality of life (QoL) scales do not directly assess QoL or the perceived impact of asth- ma on QoL. The purpose of this study is to evaluate the psychometric properties (reliability, concurrent and longitudinal validity, and responsiveness to change in asthma status) of a new measure of the patient- perceived negative effects of asthma in adults, the Asthma Impact on Quality of Life Scale (A-IQOLS), and to compare its properties with those of a measure of current QoL, the Flanagan Quality of Life Scale (QOLS). We hypothesize that the approach represented by the A-IQOLS will prove superior to that of the QOLS as an out- come measure for clinical research. This research can fill a significant gap in the currently available tools, with consequent benefit to asthma clinical research and, potentially, measurement of patient-centered outcomes in other disease areas.